Over the scatterometer record (1999–2017), the Arctic has lost more than 2 × 10⁶ km² of MYI — a decrease of more than 50%; MYI now covers less than one-third of the Arctic Ocean. Independent MYI coverage and volume records co-vary in time, the MYI area anomalies explain ~85% of the variance in the anomalies in Arctic sea ice volume. If losses of MYI continue, Arctic thickness/volume will be controlled by seasonal ice, suggesting that the thickness/volume trends will be more moderate (as seen here) but more sensitive to climate forcing.

(With the Facebook log-in down at Neven’s and not being a twitterer, I am unable to post there. So before I forget about it, I thought to put my take on Kwok (2018) on your G.W.C. site.)

The wording of Kwok (2018) is very strange, perhaps suggesting a second-language situation. My take on his comments (about the decline being “more moderate” when MYI is disappeared) is not that FYI is more resilient but that the comment is not actually talking abut the September minimum. Rather it is talking about earlier in the melt season and later in the freeze season. As it will still be cold at these times, any ice will be more difficult to melt but it is only the FYI that will be present precisely because all/almost-all the MYI has been melted out.

Kwok does make one reference when discussing FYI (as he calls it – “seasonal ice”) saying “With the large decline in MYI coverage over this record, there is a reversal in the relative contributions of the two ice types to the total area of the Arctic Ocean ice cover. Seasonal ice, having surpassed that of MYI in winter area coverage is now the dominant ice type, shifting the Arctic ice cover into a new normal where the focus on understanding processes over first-year sea are as important as those over MYI ice (Jeffries et al 2013).”

Saltier water has encroached in that area of thin sea ice north of Greenland. The situation is quite dire. In the popular discussion the “hiatus” in sea ice extent loss since 2012 has overshadowed the influx of warm salty water into the Barents and Chukchi seas and the loss of multi-year sea ice. But the decline of Arctic sea ice is continuing in the dark season months when few people are paying attention.